Gas turbine engines, such as those which power aircraft and industrial equipment, employ a compressor to compress air that is drawn into the engine and a turbine to capture energy associated with the combustion of a fuel-air mixture. An engine frequently includes one or more seals, Seals are used to isolate one or more regions of the engine. Seals help to ensure stable and efficient operation of the engine.
A piston seal is a type of seal that is frequently used in an engine. Referring to FIG. 2, a system 200 incorporating a piston seal 204 utilized in conjunction with the turbine section of the engine is shown. The piston seal 204 is shown in FIG. 2 as being slotted/seated in a groove 212 of a turbine frame vane 220.
The operating environment of the engine imposes significant requirements on the piston seal 204. For example, the operating temperature of the turbine section may approach, e.g., 870° C. in some engines. Such high/elevated temperatures may cause the material of the piston seal 204 to experience creep or stress relaxation (i.e., a decrease in stress based on a substantially equivalent amount of strain generated in a structure). Additionally, vibratory motion or energy in the engine may cause the piston seal 204 to experience significant wear. A location of the wear is denoted in FIG. 2 by dashed boxes 226 and 228.
Conventionally, the piston seal 204 has been made out of materials that include: (1) nickel-chromium alloy (e.g., Inconel X-750), and (2) a nickel-based superalloy (frequently available in commerce under the mark WASPALOY). Both of these materials have temperature limits below the aforementioned operating temperature of 870° C., such that their use in such an environment is unacceptable due to creep and/or stress relaxation. Additionally, the use of these materials fails to address the wear experienced by the piston seal 204 due to vibration. For example, chromium oxide (Cr2O3) and aluminum oxide (Al2O3) may form on a surface of the piston seal 204 during engine operation, resulting in one or more of creep, stress relaxation, or wear of the piston seal 204. In some instances, as cross-sectional area is lost to, e.g., oxidation or wear, stresses may increase. This increase in stress may tend to exacerbate/increase creep, stress relaxation, or wear. The presence of oxides can increase friction, and consequently, frictional heating. In some instances, the oxides may degrade a material of component(s) (e.g., turbine frame vane 220) that interface to the piston seal 204. Often, these component(s) are more expensive in terms of, e.g., material or manufacturing processes than the piston seal 204.